1. Field of the Invention
The present invention relates to a hydraulic supply system for a hydraulically-actuated automatic transmission.
2. Description of the Related Art
FIG. 2 shows a longitudinal cross section of a conical disk pair subassembly of a known belt-driven conical pulley transmission. The conical pulley subassembly includes a shaft 10, to which an axially fixed disk 12 is rigidly connected. Situated on shaft 10 and axially movable along a splined connection but non-rotatably carried by the shaft 10 is an axially movable disk 16. Conical surfaces of disks 12 and 16 face each other, between which an endless torque-transmitting means (not shown) circulates, which connects the illustrated conical disk pair with another conical disk pair (not shown) of the belt-driven conical-pulley transmission.
In a radially outer area of axially movable disk 16, on its side facing away from the conical surface, an annular cylinder 18 having two radially spaced, axially-extending walls defining a U-shaped cross section is rigidly attached. On the radially inner side of annular cylinder 18 a guide ring component 20 formed with a guide surface is rigidly attached.
Rigidly connected to shaft 10 at a distance from axially movable disk 16 is a support ring component 22, which includes a first axially-extending annular projection 24 that is designed on its free face with circumferentially distributed first ramp surfaces 26. Radially outwardly of the first annular projection 24, support ring component 22 includes a second axially-extending annular projection 28 that extends between the walls of annular cylinder 18. Second annular projection 28 is movable within annular cylinder 18 and includes seals, so that an adjusting chamber 30 is formed between second projection 28 and annular cylinder 18, which chamber is chargeable with hydraulic fluid through radial bores 32 in axially movable disk 16 and shaft 10, as well as a supply bore 34 extending within shaft 10.
Between support ring component 22 and axially movable disk 16, an annular sensing piston 36 is guided on shaft 10 so that it can move axially. Sensing piston 36 is generally cup-shaped, having an opening that faces in the direction of axially movable disk 16 and that ends in a ring 38, on whose side facing away from axially movable disk 16 two circumferentially spaced ramp surfaces 40 are formed. Between the first ramp surfaces 26 and the second ramp surfaces 40 rolling elements 42 are situated, which extend through cutouts formed in the sensing piston 36. The axial position of rolling elements is determined primarily by ramp surfaces 26, 40 and the radial position is determined primarily by guide surfaces 43 formed on guide ring component 20, coordinated with the ramp surfaces, as well as a radially outer surface of an axial extension of axially movable disk 16.
Between sensing piston 36 and axially movable disk 16 a torque sensing chamber 44 is formed, which is connected via radial feeder bores 46 formed in shaft 10 to a supply bore 48 extending through the shaft. Radial discharge bores 50 extend from torque sensing chamber 44 into a discharge bore 52 formed within the shaft.
On its side facing away from axially movable disk 16, sensing piston 36 has axially extending arms 54 that are situated at uniform intervals around the circumference. Arms 54 extend through openings formed in support ring component 22 and are formed with outer teeth 56 that mesh with inner teeth 58 of a drive gear 60, which is supported on shaft 10 and through which the transmission is driven. Sensing piston 36 is thus connected to drive gear 60, rigidly in the circumferential direction and is axially movable relative to the latter.
The construction and function of the conical pulley subassemblies described by way of example are known, and therefore will not be explained in detail. In consequence of rotation of sensing piston 36 relative to the support ring component 22, the axial position of sensing piston 36 changes as a result of corresponding shaping of ramp surfaces 26, 40, and of guide surfaces 43, and in such a way that when torque is high the sensing piston increasingly closes a discharge opening 61 from which radial discharge bore 50 extends, so that the hydraulic pressure in torque sensing chamber 44 increases, and axially movable disk 16 is subjected to a torque-dependent pressure in the direction toward fixed disk 12. The shift of axially movable disk 16 that is necessary to change the transmission ratio is accomplished by changing the pressure in adjusting chamber 30.
When the transmission is used in a motor vehicle, the delivery of hydraulic pressure to adjusting chamber 30 and to torque sensing chamber 44 is normally accomplished by a hydraulic pump that is driven by an internal combustion engine that serves to propel the vehicle. In order to reduce fuel consumption and improve environmental friendliness, modern motor vehicles are equipped with stop-start systems in which the internal combustion engine is automatically shut down in operating phases in which it is not needed for propelling the vehicle, for example when decelerating, when stopped at a traffic signal, or in stop-and-go traffic. The problem arises here that the supply of hydraulic pressure or hydraulic fluid to the belt-driven conical-pulley transmission is not ensured when the internal combustion engine or the pump is stopped, since when the pump is stopped the pressure in the adjusting chamber and the torque sensing chamber drops off rapidly due to leakage losses, or because hydraulic fluid drains from the adjusting chamber. The transmission is then no longer operable when the vehicle is to resume motion. Upon restarting the pump or the internal combustion engine, a certain period of time passes before the transmission is again supplied acceptably with hydraulic fluid; that can lead to dangerous situations, and during that time the transmission can be damaged by insufficient contact pressure against the endless torque-transmitting means.
An object of the present invention is to provide a remedy for the above-identified problems.